I'm not sure about most of your questions, but you might want to try Appmobi. They claim using it significantly increases rendering speed, physics calculations and has multi channel audio. I haven't used it though, so I'm not sure about how easy it is to use.ppmobi seams interresting, however I don't want to spend loads of money on it, and it seems to be a bit complicated.
Construct 2 is fairly easy to understand. Isn't there any way the developers will improve the performance? I mean, if Appmobi does it 5(?) times better than usual html5-apps, why can't construct 2?
Yes you are correct(I think), the larger the canvas then FPS will drop a little. Also if your game heavily relies on physics then the FPS will drop.
Its also to do with graphics, If you have graphics of a Higher DPI then if you have a every tick event and are manipulating that object, then its likely to be quite expensive in VRAM.Then I'll try using a resolution of 960x640.
I always try to optimize the graphics also, but how does one optimize the DPI?
And I know performing an action every tick isn't the smartest, but it seems to me it is the only way to go if you want f.e an object to constantly move in one direction? Or am I wrong?